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docs/pre13-low-c1.md

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+# Pre13 L-C1
+
+This batch aligns the endian type vocabulary of named multi-byte on-disk
+fields with the corresponding Linux EROFS declarations.
+
+Only fields for which the same Linux structure and field use `__le16`,
+`__le32`, or `__le64` were changed. Byte fields, arrays, field order, unions,
+packing, macros, and all read/conversion sites remain unchanged. The direct
+disk-type parameter of `erofs_xattr_ibody_size()` was synchronized.
+
+The FreeBSD compatibility aliases map each `__leXX` type to the exact previous
+unsigned integer type. A host-side probe compared 119 structure/union
+size/alignment and named-field offset entries before and after the batch; all
+values were identical. `tests/pre13_ondisk_layout_probe.c` retains legacy
+definitions and exhaustive assertions for every modified structure so the
+same proof can be compiled with the final FreeBSD guest toolchain. Existing
+kernel `_Static_assert` checks remain unchanged.
+
+No KLD build, QEMU, smoke, or feature test was run for this batch.